This invention relates to the structure of an internal combustion engine having a plurality of cylinder banks, and more particularly to the structure of an internal combustion engine for a vehicle suitable for use as an internal combustion engine of the V-shaped arrangement (V-type engine). 2) Description of the Related Art
In recent years, an apparatus for an OHC (overhead camshaft) engine for use with an automobile or a like vehicle has been developed wherein a valve operating system for operating an intake valve or an exhaust valve is operated to vary the operating timing or the lift amount (which will be hereinafter referred to generally as valve timing) of the intake or exhaust valve.
In the apparatus of the type described above, for example, a cam for a high speed and another cam for a low speed are provided on a camshaft and selectively used to obtain an operation timing of the intake or exhaust valve in accordance with an operating condition of the engine.
The high speed cam has a cam profile which can provide an operation timing suitable for high speed operation, and the low speed cam has another cam profile which can provide an operation timing suitable for low speed operation.
In a cam apparatus of the rocker arm type, the selection mechanism between the high speed cam and the low speed cam is constructed such that a pair of rocker arms are selectively connected to or disconnected from each other so that the valve is operated alternatively by the high speed cam or the low speed cam in order to obtain an operation timing of the intake or exhaust valve in accordance with an operation condition of the engine.
FIGS. 31 to 33 show an exemplary one of conventional valve operating systems (variable valve timing mechanisms) for selectively operating a high speed cam and a low speed cam.
Referring first to FIG. 31, the valve operating system shown includes three cams 102, 103 and 202, a pair of valves 101 serving as operated members, and three rocker arms 104, 105 and 204 interposed between the cams 102, 103 and 202 and the valves 101, respectively, and serving as arm members.
Here, the cams 102 and 202 serve as low speed cams while the cam 103 serves as a high speed cam, and the rocker arms 104 and 204 serve as low speed rocker arms operated by the cams 102 and 202, respectively, while the rocker arm 105 serves as a high speed rocker arm operated by the cam 103.
The rocker arms 104, 105 and 204 are supported for pivotal motion on a rocker shaft 106 so that they are individually rocked around the rocker shaft 106 by cam lifts of the cams 102, 103 and 202, respectively.
The low speed rocker arms 104 and 204 and the high speed rocker arm 105 are connected to or disconnected from each other by way of a pair of pistons 107 and 108 and a stopper 109.
In particular, referring also to FIGS. 32 and 33, the pistons 107 and 108 and the stopper 109 are accommodated in cylinders 204a, 105a and 104a formed coaxially in the rocker arms 204, 105 and 104, respectively, while they contact serially with each other in this order. Oil passages 106a and 204b are formed in the rocker shaft 106 and the rocker arm 204, respectively, and when oil is supplied into a space at an end portion Of the cylinder 204a by way of the oil passages 106a and 204b, the pistons 107 and 108 and the stopper 109 are moved forwardly (leftwardly in FIGS. 32 and 33) to couple the low speed rocker arms 104 and 204 and the high speed rocker arm 105 to each other, but when the oil is discharged from the space, the pistons 107 and 108 and the stopper 109 are moved rearwardly (rightwardly in FIGS. 32 and 33) by a biasing force of a return spring 110 to cancel the coupling between the low speed rocker arms 104 and 204 and the high speed rocker arm 105. The high speed rocker arm 105 is normally biased upwardly by a return spring 111.
With the variable valve timing mechanism of the construction described above, when the engine operates at a low speed, oil is discharged from the space at the end portion of the cylinder 204a so that the pistons 107 and 108 and the stopper 109 are moved rightwardly in FIG. 32 by the return spring 110 until they are accommodated into the rocker arms 204, 105 and 104, respectively. Consequently, the high speed rocker arm 105 and the low speed rocker arms 104 and 204 are disconnected from each other.
As a result, the cam profile of the low speed cam 102 is rendered effective.
On the other hand, when the engine operates at a high speed, oil is supplied into the space at the end portion of the cylinder 204a as seen from FIG. 33 so that the pistons 107 and 108 and the stopper 109 are moved leftwardly in FIG. 33 by the pressure of the oil.
Consequently, the pistons 107 and 108 connect the low speed rocker arms 204 and 104 to the high speed rocker arm 105, respectively.
Since the cam lift of the high speed cam 103 is greater than the cam lift of the low speed cams 102 and 202, the low speed cams 102 and 202 are spaced from and do not operate the respective low speed rocker arms 104 and 204, and the variable valve timing mechanism operates only with the high speed cam 103.
Where the variable valve timing mechanism which can Vary the valve timing in this manner is employed for an engine of an automobile or a like vehicle, a valve timing suitable for an operation condition of the engine can be provided. Multi-cylinder engines have been realized which include a plurality of variable valve timing mechanisms of a same construction provided for individual cylinders and cause the variable valve timing mechanisms to operate similarly to each other across a certain operation condition of the engine (for example, the speed of rotation of or the load to the engine) to vary the performances of the valves.
Also multi-cylinder internal combustion engines (multi-cylinder engines) having a plurality of cylinder banks have been proposed which include means for differentiating the valve timings of the intake valves or the exhaust valves of the engine from each other among the different cylinders using a plurality of sets of valve operating mechanisms for variable valve timing mechanisms of the engine having different characteristics from each other to adjust the rotating condition of the engine finely to improve the output power or the fuel consumption of the engine.
FIGS. 34 and 35 show valve operating apparatus disclosed in Japanese Patent Laid-Open Application No. Heisei 3-57284. Particularly, FIG. 34 shows a valve operating apparatus for a four-cylinder engine. In the engine shown, valves 101 and 201 of first and fourth cylinders C1 and C4 are operated to be opened and closed each by a valve operating mechanism 40a including a variable valve timing mechanism while valves 101 and 201 of second and third cylinders C2 and C3 are operated to be opened and closed each by another valve operating mechanism 40b having another variable valve timing mechanism different from that of the valve operating mechanism 40a.
Each of the valve operating mechanisms 40a includes first and third rocker arms 41 and 43a which do not contact with any cam and a second rocker arm 42 which slidably contacts with a high speed cam 103. The first and third rocker arms 41 and 43a and the second rocker arm 42 are supported for pivotal motion on a rocker shaft 106 such that they can be connected to and disconnected from each other. The second rocker arm 42 is located between the first rocker arm 41 and the third rocker arm 43a. The valve 101 is operated by the first rocker arm 41 while the valve 201 is operated by the third rocker arm 43a. Change-over between connection and disconnection of the rocker arms 41, 42 and 43a is performed by forward and rearward movement, respectively, of piston pins not shown by a hydraulic pressure similarly as in the variable valve timing mechanism described above.
Meanwhile, each of the other valve operating mechanisms 40b includes a first rocker arm 41 which does not contact with any cam, a second rocker arm 42 which slidably contacts with a high speed cam 103, and a third rocker arm 43b for slidably contacting with a low speed cam 102. The first, second and third rocker arms 41, 42 and 43b are supported for pivotal motion on the rocker shaft 106 such that they can be connected to and disconnected from each other. The valve 101 is operated by the first rocker arm 41 while the valve 201 is operated by the third rocker arm 43b. Change-over between connection and disconnection of the rocker arms 41, 42 and 43b is performed by forward and rearward movement, respectively, of piston pins not shown by a hydraulic pressure similarly as in the variable valve timing mechanism described above.
In the engine of the construction described above, when the engine operates at a low speed, the rocker arms 41, 42 and 43a in each of the first and fourth cylinders C1 and C4 are disconnected from each other, and consequently, the valve 101 connected to the first rocker arm 41 and the valve 201 connected to the third rocker arm 43a are not operated and are held closed so that the first and fourth cylinders C1 and C4 are at rest or inoperative.
Meanwhile, also in each of the second and third cylinders C2 and C3, the rocker arms 41, 42 and 43b are disconnected from each other, and consequently, the valve 101 connected to the first rocker arm 41 is not operated and is held closed while the valve 201 connected to the third rocker arm 43b is operated to open and close at a valve timing in accordance with the profile of the low speed cam 102.
Accordingly, when the engine operates at a low speed, the first and fourth cylinders C1 and C4 of the total four cylinders are in a rest condition while the valves 201 of the remaining second and third cylinders C2 and C3 are operated to open and close in accordance with the low speed cams 102.
On the other hand, when the engine operates at a high speed, in each of the first and fourth cylinders C1 and C4, the rocker arms 41, 42 and 43a are connected to each other so that they are rocked integrally with each other, and consequently, the valves 101 and 201 are operated to open and close at a timing and by a lift amount provided by the profile of the high speed cam 103.
Also in each of the second and third cylinders C2 and C3, the rocker arms 41, 42 and 43b are connected to each other so that they are rocked integrally with each other, and consequently, the valves 101 and 201 are operated to open and close at a timing and by a lift amount provided by the profile of the high speed cam 103.
Accordingly, upon high speed operation of the engine, all of the four cylinders operate in an operating condition provided by the high speed cams 103, and consequently, the output power of the engine is increased.
It is to be noted that reference numeral 1 in FIG. 34 denotes a cylinder head.
Referring now to FIG. 35, there is a valve operating apparatus for a six-cylinder engine. In the engine shown, valves 101 and 201 of first and sixth cylinders C1 and C6 are each operated by a valve operating system 40d; valves 101 and 201 of second and fifth cylinders C2 and C5 are each operated by another valve operating system 40b; and valves 101 and 201 of third and fourth cylinders C3 and C4 are each operated by a valve operating mechanism 40c. Here, the valve operating mechanisms 40b, 40c and 40d are each provided with a variable valve timing mechanism. In this manner, the six-cylinder engine includes three sets of valve operating mechanisms incorporated therein, and the sixth cylinder is paired with the first cylinder; the fifth cylinder is paired with the second cylinder: and the fourth cylinder is paired with the third cylinder.
Each of the valve operating mechanisms 40d includes a first rocker arm 141 which slidably contacts with a low speed cam 102, a second rocker arm 142 which does not slidably contact with any cam but is connected to two valves 101 and 201, and a third rocker arm 43 which slidably contacts with a high speed cam 103. The first, second and third rocker arms 141, 142 and 43 are supported for pivotal motion on a rocker shaft 106 such that they can be connected to and disconnected from each other. The second rocker arm 142 is disposed between the first and third rocker arms 141 and 43. The first and second rocker arms 141 and 142 can be connected to each other by supply of oil of a comparatively low pressure, and when they are connected to each other, the second rocker arm 142 is rocked by and integrally with the first rocker arm 141. Meanwhile, the second and third rocker arms 142 and 43 can be connected to each other by supply of oil of a comparatively high pressure, and when they are connected to each other, the second rocker arm 142 is rocked by and integrally with the third rocker arm 43.
Meanwhile, each of the valve operating mechanisms 40b includes a first rocker arm 41 which does not slidably contact with any cam but is connected to a valve 101, a second rocker arm 42 which slidably contacts with a high speed cam 103 and a third rocker arm 43b which slidably contacts with a low speed cam 102 and is connected to another valve 201. The first, second and third rocker arms 41, 42 and 43b are supported for pivotal motion on the rocker shaft 106 such that they can be connected to and disconnected from each other. Accordingly, the two valves 101 and 201 are individually connected for interlocking motion to the first and third rocker arms 41 and 43b, respectively.
On the other hand, each of the valve operating mechanisms 40c includes first, second and third rocker arms 41, 42 and 43b disposed in a similar manner as in the valve operating mechanisms 4Ob. But here, the first and second rocker arms 41 and 42 are connected to each other by supply of oil of a comparatively low pressure, and the second and third rocker arms 42 and 43b are connected to each other by supply of oil of a comparative high pressure.
Accordingly, when the engine operates at a low speed, the first, second and third rocker arms 141, 142 and 43 of each of the first and sixth cylinders C1 and C6 are disconnected from each other, and consequently, the second rocker arm 142 to which the two valves 101 and 201 are connected is not rocked. As a result, the first and sixth cylinders C1 and C6 are at rest.
Also in each of the second and fifth cylinders C2 and C5, the first, second and third rocker arms 41, 42 and 43b are disconnected from each other, and consequently, the valve 101 to which the first rocker arm 41 is connected is at rest while the valve 201 connected to the third rocker arm 43b is operated to open and close at a timing and by a lift amount provided by the profile of the low speed cam 102.
Also in each of the third and fourth cylinders C3 and C4, the first, second and third rocker arms 41, 42 and 43b are disconnected from each other, and consequently, the valve 101 connected to the first rocker arm 41 is at rest while the valve 201 connected to the third rocker arm 43b is operated to open and close at a timing and by a lift amount provided by the profile of the low speed cam 102.
When the engine operates at an intermediate speed, the first and second rocker arms 141 and 142 in each of the valve operating mechanisms 40d and the first and second rocker arms 41 and 42 in each of the valve operating mechanisms 40c are individually connected to each other.
Accordingly, in each of the first and sixth cylinders C1 and C6, the two valves 101 and 201 connected to the second rocker arm 142 are operated to open and close at a timing and by a lift amount provided by the profile of the low speed cam 102.
Meanwhile, in the second and fifth cylinders C2 and C5, the connecting conditions of the rocker arms 41, 42 and 43b in each of the valve operating mechanisms 40b are the same as those when the engine operates at a low speed. Thus, the valve 101 connected to the first rocker arm 41 is at rest while the valve 201 connected to the third rocker arm 43b is operated to open and close at a timing and by a lift amount provided by the profile of the low speed cam 102.
Further, in each of the third and fourth cylinders C3 and C4, the first and second rocker arms 41 and 42 in each of the valve operating mechanisms 40c are connected to each other, and consequently, the valve 101 connected to the first rocker arm 41 is operated to open and close at a timing and by a lift amount provided by the profile of the high speed cam 103 while the valve 201 connected to the third rocker arm 43b is operated to open and close at a timing and by a lift amount provided by the profile of the low speed cam 102.
When the engine operates at a high speed, the rocker arms 141, 142 and 43 of each of the valve operating mechanisms 40d are connected to each other, and also the rocker arms 41, 42 and 43b of each of the valve operating mechanisms 40b are connected to each other. Also the rocker arms 41, 42 and 43b in each of the valve operating mechanism 40c are connected to each other.
Accordingly, the valves 101 and 201 of all of the cylinders C1 to C6 are each operated to open and close at a timing and by a lift amount provided by the high speed cam 103.
In particular, in the first and sixth cylinders C1 and C6, the second rocker arm 142 is rocked by and integral with the third rocker arm 43, and consequently, the two valves 101 and 201 connected to the second rocker arm 142 are operated to open and close at a timing and by an amount provided by the profile of the high speed cam 103.
Meanwhile, in the second and fifth cylinders C2 and C5, the rocker arms 41, 42 and 43b are rocked by and integral with the high speed cam 103, and consequently, the valves 101 and 201 connected to the first and third rocker arms 41 and 43b are operated to open and close at a timing and by an amount provided by the profile of the high speed cam 103.
Further, also in the third and fourth cylinders C3 and C4, similarly as in the second and fifth cylinders C2 and C5, the rocker arms 41, 42 and 43b are rocked by and integral with the high speed cam 103, and consequently, the valves 101 and 201 connected to the first and third rocker arms 41 and 43b are operated to open and close at a timing and by a lift amount provided by the profile of the high speed cam 103.
It is to be noted that those mechanisms are applied to both of the intake valves and the exhaust valves.
By incorporating a plurality of sets of different valve operating mechanisms for different cylinders in this manner, each of the valve operating mechanisms can vary valve timings of an intake valve and an exhaust valve in response to the speed of rotation of and/or the load to the engine and can cause intake valves or exhaust valves of a certain set of cylinders (for example, the set of the first and sixth cylinders in the case of the engine described above) to operate at valve timings different from those of intake valves or exhaust valves of the other sets of cylinders under a certain condition of the engine.
Accordingly, by varying the operation forms of the intake valves or exhaust valves of the different cylinders in response to an operation condition of the engine, the output power of the engine is controlled finely and the fuel consumption is improved.
Meanwhile, it is also possible to apply the structure, wherein a plurality of types of valve operating systems is assembled on a single engine in this manner, to an engine of the type having a plurality 10 of cylinder banks such as, for example, a V-type engine.
In this manner, in an engine of the type which includes a plurality of cylinder banks, the arrangement, the combination and so forth of valve operating systems have an influence upon various aspects of the automobile such as, for example, the facility of assembly of the engine described above, maintenance and so forth of the engine and the performance of a catalyzer for exhaust gas purification provided for the engine. Also subjects peculiar to an engine having a plurality of cylinder banks are provided with regard to the intake system and the exhaust system.
In particular, the conventional valve operating mechanism described above is complicated in structure. Besides, where different valve operating mechanisms of the conventional structure are incorporated in different cylinders of a multi-cylinder engine, there are a problem to be solved that, upon assembly of the engine, an operator may possibly assemble parts in error and another problem that a long period of time is required for assembly of the engine and the production efficiency is low.
In this connection, it is considered that a unique solution or solutions be available with an engine having a plurality of cylinder banks.
Further, in an engine, for example, in a V-type engine, it is necessary to assure a certain length for an intake pipe. To this end, it seems a promising means to dispose part of the intake pipe in an overhanging condition above the cylinder head.
However, it is considered that, in a V-type engine provided with a variable displacement mechanism, a cylinder block for a cylinder provided with a variable displacement mechanism is complicated in structure and high in frequency for maintenance compared with another cylinder block for another cylinder provided with no variable displacement mechanism. Therefore, if intake pipes are disposed in an overhanging condition above the cylinder blocks of a V-type engine as described above, then there is a subject that the facility of maintenance of the cylinder blocks of cylinders each provided with such a variable displacement mechanism as described above is deteriorated by the intake valves.
Further, where the intake valves partially overhang above the cylinder head as described above, there is another subject that, when it is tried to adjust the valve clearances, for example, at cylinder head portions located below the intake valves, the intake pipes may disturb such operation, and consequently, it is difficult to perform management of the valve clearances.
Further, a vehicle such as an automobile normally includes a catalytic converter installed thereon for purifying exhaust gas exhausted from the engine. Such catalytic converter is normally provided on a route of exhaust gas extending from the engine to the muffler (silencer) and includes a purifying catalyzer for reducing the concentration of CO (carbon oxide), HC (hydrocarbon), NOx (nitrogen oxides) and like chemicals contained in the exhaust gas.
FIG. 36 shows the relationship between the purifying efficiency of a catalytic converter and the temperature of exhaust gas. As seen from FIG. 36, the purifying efficiency of the catalytic converter is higher when the temperature of the exhaust gas is high, and when the temperature of the exhaust gas is low, the exhaust gas is not purified efficiently. Accordingly, the catalytic converter is installed, in the exhaust gas route, at a location in the proximity of an exhaust manifold in which the temperature of the exhaust gas is comparatively high.
Meanwhile, an engine provided on a vehicle is popularly cooled by cooling wind such as running wind, and a cylinder which is blown directly by cooling wind is cooled to a large extent. Therefore, when some of cylinders of an engine provided with a variable displacement mechanism are rendered inoperative, the temperature of exhaust gas is lowered by running wind and/or cooling wind produced by a radiator cooling fan, resulting in deterioration of the purifying efficiency of the catalytic converter. Consequently, there is a problem that purification of exhaust gas cannot be performed sufficiently.